A printed circuit, also known by the acronym PCB (Printed Circuit Board), is a support that makes it possible to electrically link a set of electrical components. Such a printed circuit generally takes the form of a laminated plate. This printed circuit can be single-layer or multi-layer.
A single-layer printed circuit comprises only a single metallization layer in which are printed conductive tracks that electrically connect the different electrical components together. A multilayer printed circuit comprises, on the other hand, a plurality of metallization layers, that is to say at least two layers and, preferably, more than four or six layers. Hereinafter in this description, these multilayer printed circuits will be the focus of interest.
A metallization layer is one of the layers of the laminated plate forming the printed circuit in which are produced one or more conductive tracks that electrically connect the different electrical components together. This layer is planar and extends parallel to the plane of the laminated plate. Generally, the metallization layer is obtained by depositing a uniform layer of a conductive material, typically a metal such as copper, then etching this uniform layer to leave only the conductive tracks remaining.
The different metallization layers of the printed circuit are spaced apart mechanically from one another by insulating layers made of electrically insulating material. This insulating material exhibits a high dielectric strength, that is to say typically greater than 3 MV/m and, preferably, greater than 10 MV/m. For example, the electrically insulating material is produced from epoxy resin and/or glass fiber. The insulating layer generally takes the form of a rigid plate produced in a material that does not become viscous during its assembly with other layers. For example, it is produced from a thermosetting resin that has already undergone an irreversible thermosetting process.
The different layers of the multilayer printed circuit are assembled together, with no degree of freedom, using adhesive layers familiarly called “prepreg.”
A prepreg consists of a thermosetting resin impregnating, generally, a reinforcement such as a fabric. Typically, the resin is an epoxy resin. During the fabrication of the printed circuit, the transformation of the thermosetting resin involves an irreversible polymerization that transforms the prepreg into a solid and rigid material that irreversibly bonds together the different layers of the printed circuit. Typically, each transformation occurs when the prepreg is heated to a high temperature and is compressed with a high pressure. Here, a high temperature is a temperature greater than 100° C. and, preferably, greater than 150° C. A high pressure is a pressure greater than 0.3 MPa and, typically, greater than 1 MPa.
The conductive tracks of the different metallization layers can be electrically connected via conductive bump contacts or pads passing through the insulating layers. The conductive bump contacts or pads are better known as “vias.” The vias generally extend at right angles to the plane of the layers. There are different ways of fabricating these vias. One of the most common ways is to produce a hole in the insulating layer or layers to pass through and then to cover the inner wall of these holes with a metal. These are called metalized holes.
A via does not necessarily pass through all the layers of the printed circuit. Thus, there are blind vias that emerge on a single outer face of the printed circuit. These days, it is also possible to produce “buried” vias for example, using known technologies such as the technology known by the acronym HDI (High Density of Integration). A buried via does not emerge on any of the outer faces of the printed circuit. For example, a buried via makes it possible to electrically connect conductive tracks produced in metallization layers embedded inside the printed circuit.
A known current sensor, is for example disclosed in O'Donnell, et al., “Planar fluxgate current sensor integrated in printed circuit board”, Sensors and Actuators A 129 (2006) 20-24.
This current sensor operates well. For example, periodically saturating the magnetic core makes it possible to measure the contribution of the magnetic field Bi generated by the current to be measured at high frequencies and increases the dynamic range of the sensor. High frequency means a frequency of greater than 100 Hz and, preferably, greater than 1 kHz. This measurement technique is known by the term “fluxgate sensor.” However, for this sensor to operate well, it is necessary to be capable of precisely compensating for the contribution of the magnetic excitation field Bex generated inside the core by the excitation coil. Accordingly, the conducting wire must be positioned precisely with respect to the magnetic core. This problem has been solved in known sensors by producing a conducting track in the printed circuit and in which the current to be measured flows. Indeed, with present-day technologies, it is possible to position a conducting track of a printed circuit very precisely. However, when using this sensor, it is necessary to link the conducting wire to this conducting track of the printed circuit. This makes it necessary to provide for connection terminals on the printed circuit, thereby increasing the bulk of the current sensor. This also requires systematic cutting of the conducting wire in which the current to be measured flows, this not always being desirable.